Web IM platforms are now popular among Internet users as an indispensable tool for communications. Fundamental data maintained by an IM platform is about a group of users whom a user cares about and who communicate directly with the user via instant messaging, and the group of users are referred to as the user's “buddies”. As the time spent by the user in communicating via the IM platform increases, a large number of buddies may be accumulated in the user's buddy list, and an IM user terminal presents the buddies in a list form to the user. For an IM system, each buddy in a buddy list has the same position and importance with the others, and has no difference from the others. But the user may have different concerns for different buddies and may concern different aspects for different buddies, and the differences may have impact on a pattern adopted by the user to classify the buddies.